Pressure-responsive electric switch

ABSTRACT

The invention relates to a snap action electric switch assembly having fluid pressure operated means for biasing the lever means in the direction opposite the biasing force of the snap action spring in response to pressurized fluid being directed to the chamber.

Field of Search ..200/830, 83 P, 67 D o v I United States Patent 1 [111 3,729,605 Andresen [4 1 Apr. 24, 1973 [54] PRESSURE-RESPONSIVE ELECTRIC [56] References Cited SWITCH UNITED STATES PATENTS [75] Inventor: Jens Nicolai, Andresen, Nordborg,

Denmark 3,609,270 9/1971 Sonderborg ZOO/ 670 2,738,397 3/1956 Slonneger ..200/83 P [73] Assignee: Danfoss A/S, Nordborg, Denmark Primary ExaminerRobert K. Schaefer [22] Flled' 1972 Assistant Examiner-Gerald P. Tolin [21] Appl. No.: 215,489 Att0rney-Wayne B. Easton [30] Foreign Application Priority Data [57] ABSTRACT The invention relates to a snap action electric switch Jan 12, l9' 7l Germany ..P2l 0] 196.1 assembly having fluid pressure operated means for biasing the lever means in the direction opposite the 1 [52] Cl "200/83 200/83 200/67 D biasing force of the snap action spring in response to Int. Cl. pressurized being directed to h chamber.

1 Claim, 2 Drawing Figures PRESSURE-RESPONSIVE ELECTRIC SWITCH The invention relates to a pressure-responsive elec tric switch with an operating element which acts on a two-part'snap-action system, consisting of a lever and a snap-action spring, and against which element a spring force acts, the switch also having a casing.

An electric thermostat switch is known in which an operating element, subjected to the pressure of saturated steam, and a cylindrical rated-value spring, arranged coaxially with said element, act on'a rod which in turn engages a rigid lever of the snap-action system. The arrnagement isaccommodated in a sheet-metal casing to which is riveted a sheet-metal strip which acts as a bearing for the snap-action spring. This arrangement is complicated, large and expensive.

Also known is a bimetal switch in which the bimetal, firmly clamped at one end, together with a bent snapaction spring constitutes the snap-action system. An extension connected to the snap-action spring acts upon the movable contact, which in the at-rest position is pressed against the fixed contact by its own spring force.

The object of the invention is to provide a pressureresponsive electric switch of the initially described kind, for example a thermostat or a pressostat, which may be of very small design and very cheap to produce.

According to the invention, this object is achieved by the lever itself taking the form of a spring and being secured at one end to the side walls of the casing, by the snap-action spring being mounted on a bearing formed on an end face of the casing, and by the operating element, designed as a pressure element, being secured to the base of the casing and connected to the lever by way of a plunger.

In this construction there is no need for a separate rated-value spring, since'the function of this is performed by the lever of thesnap-action system. It is therefore also unnecessary for such rated-value springs to be arranged co-axially with the operating element. The casing directly supports all the important working elements, i.e.,;the lever, the snap-action spring and the pressure element. This results in an unusually inexpensive construction. Nevertheless, any required function may be allotted to the switch, since any desired bias may be imparted to the resilient lever during manufacture and because the balance of the switch can be adjusted as required with the aid of the bearing for the snap-action spring formed on the casing. The switch may also be of very small design and, excluding the connecting port for the pressure element, may have dimensions of 13 X 16 X 36mm for instance.

It will generally suffice if the casing is constituted by a sheet-metal part bent to the shape of a U and has only one end wall. This results in an extremely inexpensive component.

A set of central contacts may be fitted between the lever and the bottom of the casing, the moving contact being connected to the lever through an actuating element. In this way, the free space required in the casing on account of the length of the lever is economically utilized.

The vasin g may perform further functions. For exam- 1 pie one of the stops for the snap-action system may be formed on the side wall of the casing. Both stops may of course also be formed there.

Biasing is expediently achieved by bending the lever forward in the direction of the operating element at that end of thelever whereby it is secured.

In order to fit the lever properly and to enable it to be firmly secured in the casing, it is advantageous if the casing contains inclined slots each with a stepped locking portion for securing to tabs on the lever, the slots being closed up after the lever has been fitted therein.

The invention will now be described in greater detail by reference to an embodiment illustrated in the drawing, in which:

FIG. 1 is a schematic section through a switch in accordance with the invention, and

FIG. 2 is an end view of the switch of FIG. 1, as seen at the side where the set of contacts is located.

In the embodiment illustrated, there is provided a casing l, which has a base 2, side walls 3 and 4 and an end wall 5. Provided at the base is a port 6, with a pressure element 7 which comprises a diaphragm 8. A passage 9 leads to the cavity 10 of the pressure element. A plunger 11 extends through an opening 12 into the interior of the casing.

A snap-action system consists of a lever 13, which takes the form of a spring, and of a snap-action spring 14 having the shape of the Greek letter omega. The latter is mounted between the free end 15 of the lever 13 and a tab 16 which is formed on the end wall 5 of the casing.

The lever 13 has a rear end 15 which is clamped in the casing and is bent forward from the rest of the lever in the direction of the pressure element 10, to an extent depending upon the required rated-value. For the purpose of securing it, the lever 13 has two lateral tabs 18 and 19 which are inserted in inclined slots 20. Each of the inclined slots merges with a stepped locking portion 21. When the tabs 18 and 19 are introduced into the portion 21, the upper part 22 of the casing can be depressed so that the lever 13 is firmly held.

A contact insert 23 is fitted into the space between the lever 13 and the base 2.0fthe casing. This insert contains an insulating block 24 in which are secured on the one hand a carrier 25 for a fixed contact 26 and on the other a contact spring 27 with a movable contact 28, the insulating block also carrying the associated connector 29. An actuating element 30 having a collar 31 extends through an opening in the lever 13, an opening in the insert 23 and an opening in the contact spring 27.

Furthermore, stops 32 are formed on the side walls 3 and 4, these stops limiting the upward movement of the snap-action system.

In the position illustrated, the bias of the resilient lever 13 preponderates, and the downwardly directed force component of the snap-action spring 14 overcomes the force applied by the pressure element 7. The actuating element 30 is consequently pressed into its lower end position in which the collar 31 bears on the insert 23 and movable contact 28 is separated from the fixed contact 26. If the pressure in the pressure unit now rises to a lever that exceeds the force component of the rated-value spring 14, then the system snaps suddenly over into the upper end position in which the lever 13 bears against the stops 32. Before the upper end position has, been reached, the mass of the snap-action system becomes separated from the contact spring 27 and the movable contact 28, so that only the small mass of this contact strikes the fixed contact 26. If the pressure in the pressure unit 7 falls, the system snaps back into the initial position as illustrated when a predetermined pressure-difference has been passed through, and the movable contact 28 is only separated from the fixed contact 26 after the actuating element 30 has travelled a certain distance, so that sudden separation of the contacts takes place.

The pressure-difference can be adjusted by bending the tab 16. The rated-value can be adjusted by bending the lever 13.

A simple covering or the like of plastics material may be fitted over the casing to meet particular assembly requirements.

I claim:

1. A snap action electric switch assembly comprising, a frame, spaced apart abutment support means on said frame, a lever and a snap action spring between said.

spaced apart support means, said lever having a movable free end engaging said snap action spring, said snap action spring biasing said lever in one direction, fixed contact means mounted on said frame, a leaf spring attached to said frame and carrying a movable contact which is engageable with said fixed contact, an actuator element connected to said lever and to the free end of said leaf spring, fluid pressure chamber means connected to said frame, plunger means between said fluid pressure chamber means and said free end of said lever for biasing said lever in the direction opposite from said one direction in'response to said chamber means being pressurized. 

1. A snap action electric switch assembly comprising, a frame, spaced apart abutment support means on said frame, a lever and a snap action spring between said spaced apart support means, said lever having a movable free end engaging said snap action spring, said snap action spring biasing said lever in one direction, fixed contact means mounted on said frame, a leaf spring attached to said frame and carrying a movable contact which is engageable with said fixed contact, an actuator element connected to said lever and to the free end of said leaf spring, fluid pressure chamber means connected to said frame, plunger means between said fluid pressure chamber means and said free end of said lever for biasing said lever in the direction opposite from said one direction in response to said chamber means being pressurized. 